Visible light and IR combined image camera

ABSTRACT

A camera producing visible light images with thermal data. The camera may include visible light lens and sensor, an infrared light lens and sensor, and a display. The display displays some of the visible light image and thermal data from the respective sensors. The visible light image is divided into an array of zones where each zone may provide thermal data associated with the corresponding portion of the target shown in the zone. The camera may sense infrared images also provide audible alarms where the alarm is emitted with a tone of variable output to indicate the relative level of the alarm.

RELATED APPLICATIONS

The present application is a continuation of co-pending U.S. patent.Ser. No. 12/176,853, filed Jul. 21, 2008, which is acontinuation-in-part of U.S. patent application Ser. No. 11/294,752,filed Dec. 5, 2005, now issued as U.S. Pat. No. 7,538,326, which in turnclaims priority to U.S. Provisional Patent Application No. 60/633,078,filed Dec. 3, 2004, the disclosures of which are herein incorporated byreference in their entirety.

BACKGROUND

Many infrared cameras today produce an image (IR image) of a scene usingonly energy in the far-infrared portion of the electromagnetic spectrum,typically in the 8-14 micron range. Images obtained using these camerasassign colors or gray-levels to the pixels composing the scene based onthe intensity of the IR radiation reaching the camera's sensor elements.Because the resulting IR image is based on the target's temperature, andbecause the colors or levels displayed by the camera do not typicallycorrespond to the visible light colors of the scene, it can bedifficult, especially for novice users of such a device, to accuratelyrelate features of interest (e.g. hot spots) in the IR scene with theircorresponding locations in the visible-light scene viewed by theoperator. In applications where the infrared scene contrast is low,infrared-only images may be especially difficult to interpret.

An infrared scene is a result of thermal emission and, not all, but mostinfrared scenes are by their very nature less sharp compared to visibleimages which are a result of reflected visible light. For example,considering an electric control panel of an industrial machine which hasmany electrical components and interconnections, the visible image willbe sharp and clear due to the different colors and well defined shapes.The infrared image may appear less sharp due to the transfer of heatfrom the hot part or parts to adjacent parts.

When panning an area with an infrared camera looking for hot or coldspots, one can watch the camera display for a visible color change.However, sometimes the hot or cold spot may be small and the colorchange may go unnoticed. To aid in the identification of hot or coldspots, infrared cameras often indicate the hot spot or cold spotlocation via a visible cursor or other graphical indicator on thedisplay. The temperature of such hot spots, calculated using well-knownradiometric techniques (e.g., establishing or measuring a referencetemperature), is often displayed nearby the cursor. Even with the colorchange and the hot spot indications, it can be difficult to accuratelyrelate the hot spot (or other features of interest) in the cameradisplay's IR imagery with their corresponding locations in thevisible-light scene viewed by the operator.

To address this problem of better identifying temperature spots ofinterest, some cameras allow the operator to capture a visible-lightimage (often called a “control image”) of the scene using a separatevisible light camera built into the infrared camera. The FLIR ThermaCam®P65 commercially available from FLIR Systems of Wilsonville, Oreg. is anexample of such a camera. These cameras provide no capability toautomatically align, or to merge the visible-light and infrared imagesin the camera. It is left to the operator to manually correlate imagefeatures of interest in the infrared image with corresponding imagefeatures in the visible-light image.

Alternatively, some infrared cameras employ a laser pointer that iseither built into, or affixed to the camera. The FLIR ThermaCam® E65commercially available from FLIR Systems of Wilsonville, Oreg. is anexample of such a camera. This laser pointer projects a visible point orarea onto the target, to allow the user to visually identify thatportion of the target scene that is being displayed by the infraredcamera. Because the laser pointer radiation is in the visible spectrum,it is not visible in the infrared image. As a result, the laser pointeris of limited value in infrared cameras. This can be problematic whenthe location of a hot or cold spot is difficult to identify. Forexample, large industrial control panels often have many components thatare similar in shape and packed tightly together. It is sometimesdifficult to determine the exact component that is causing a thermalevent, such as a hot spot in the infrared camera image.

Other infrared temperature measurement instruments may employ either asingle temperature measurement sensor, or a very small number oftemperature sensors arrayed in a grid pattern. Single point instrumentstypically provide a laser pointing system to identify the target area byilluminating the point or area viewed by the single temperature sensorelement, e.g. Mikron M120 commercially available from Mikron InfraredInc. of Oakland, N.J. Alternatively, some systems employ an opticalsystem that allows the user to visually identify the point in the targetscene that is being measured by the instrument by sighting through anoptical path that is aligned with the temperature sensor, e.g. MikronM90 commercially available from Mikron Infrared Inc. of Oakland, N.J.Instruments with more than one sensor element typically provide a verycrude infrared image made up of a small number of scene pixels, eachwith a relatively large instantaneous field of view (IFOV), e.g. IRISYSIRI 1011 commercially available from Advanced Test Equipment of SanDiego, Calif. It can be very difficult to accurately identify featuresof interest using such images.

It is often difficult to focus infrared images because the infraredimages do not typically have sharp resolution. For example, because ofheat transfer by multiple processes from hot locations to adjoininglocations, the images do not always have sharp resolution. This makesfocusing the infrared image user subjective. It is desirable to make thefocusing of infrared images less subjective.

SUMMARY

Certain embodiments of the invention include a camera producing visiblelight images with thermal data. The camera comprises a visible light(VL) lens, a VL sensor, an infrared (IR) lens, an IR sensor, and adisplay. The IR sensor has substantially fewer sensor elements than theVL sensor. The display can concurrently display VL images from the VLlens and sensor and thermal data from the IR lens and IR sensor. Thedisplayed VL image may be divided into an array of zones where each zonecorresponds to one of the IR sensor elements, and the thermal data isselectively displayed within the corresponding zones over portions ofthe VL image.

Certain embodiments of the invention include a camera for sensinginfrared (IR) images including an array of IR detectors and an alarmmodule. The array of IR detectors can sense IR images of a target scene.The alarm module can provide an audible alarm when a portion of thesensed IR images meets at least one user-defined alarm criterion, thealarm is emitted with a tone of variable output, where the variation ofthe output tone indicates the relative level of the alarm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are front and rear perspective views of a camera accordingto an embodiment of the invention.

FIG. 3 shows a block diagram of a representative camera system accordingto an embodiment of the invention that can be used to practiceembodiments of the invention.

FIG. 4 is a diagram showing the optical path and sensor configuration ofthe camera.

FIG. 5 shows geometrically, the derivation of the parallax equation.

FIG. 6 shows the (Full-Screen, Full-Sensor infrared)/(Full-Screen,Partial-Sensor Visible-Light) scene display mode.

FIGS. 6A and 6B show the (Full-Screen, Full-Sensorinfrared)/(Full-Screen, Partial or Full Sensor Visible-Light) scenedisplay mode according to some embodiments with small infrared arrays.

FIGS. 7 and 8 are cross-sectional views of an infrared camera modulewith a magnet and Hall-Effect sensor according to an embodiment of theinvention.

FIG. 9 shows combined visible-light and infrared images uncorrected forparallax error.

FIG. 10 shows the same images corrected for parallax error.

FIG. 11 shows the (Partial-Screen, Partial-Sensorinfrared)/(Full-Screen, Full-Sensor Visible-Light) scene display mode.In this mode, the camera uses all of the visible-light sensor elementsto fill the display.

FIG. 12 shows the (Partial-Screen, Full-Sensor infrared)/(Full-Screen,Partial-Sensor Visible-Light) scene display mode. In this mode, thecamera uses all of the available infrared sensor elements to provide aninfrared image that fills only a central area of the camera display.

FIG. 13 shows the (Partial-Screen, Full-Sensor infrared)/(Full-Screen,Full-Sensor Visible-Light) scene display mode. In this mode, the camerauses all of the infrared and all of the visible-light sensor elements toconstruct the displayed images.

FIGS. 14-16 show respectively, an infrared only image of an insulatedcup, a visible-light only image of the cup and a partial alpha-blendedimage of the cup.

FIG. 17 shows an example of a “hot threshold” alarm mode display.

FIG. 18 shows a typical infrared image of a low infrared contrast scene.

FIG. 19 shows the same scene with an alpha-blended visible-light image,yielding a much higher apparent contrast.

FIGS. 20-23 show, respectively, a visible-light image with a laser spot,a visible-light image with the laser spot and a computer generated lasermarker aligned with the laser spot, an infrared only image with thecomputer generated laser marker and hot spot not aligned, and aninfrared only image with the computer generated laser marker and hotspot aligned.

FIGS. 24-26 show, respectively, a visible-light only image with a laserpoint, an alpha-blended visible-light/infrared image with a laser pointand hot spot not aligned, and an alpha-blended visible-light/infraredimage with a laser point spot aligned.

FIGS. 27-28 show, respectively, an infrared only image with a computergenerated laser pointer and hot spot not aligned and an infrared onlyimage with the computer generated laser pointer and hot spot aligned.

FIGS. 29-30 show, respectively, a visible-light only image with a laserspot and a computer generated laser marker not aligned and avisible-light only image with the laser spot and computer generatedlaser marker aligned.

DETAILED DESCRIPTION

System Description

FIGS. 1 and 2 are perspective views of the front and the back of acamera 10 according to an embodiment of the invention. The housingincludes an infrared camera module and a visible-light camera module. Inparticular, the camera 10 includes a camera housing 12, a Visible-Light(VL) lens 13, an infrared lens 14, focus ring 16 and a laser pointer 18as well as various electronics located within the housing as will bedescribed with reference to FIG. 3. As shown, the laser pointer 18 ismounted adjacent to the VL lens 13, which, of course, creates aninsignificant or negligible parallax error between the VL lens 13 andlaser pointer 18. In an embodiment, an LED torch/flash 17 is located oneach side of the VL lens 13 to aid in providing enough light in darkenvironments. A display 20 is located on the back of the camera so thatinfrared images, visible light images and/or blended images of Infraredand Visible-Light may be viewed. In addition, target site temperature(including temperature measurement spot size) and distance readings maybe displayed. Also located on the back of the camera are user controls22 to control the display mode and activate or deactivate the laserpointer.

FIG. 3 shows a block diagram of a representative camera system accordingto an embodiment of the invention that can be used to practiceembodiments of the invention.

The Visible-Light camera module includes a CMOS, CCD or other types ofvisible-light camera, LED torch/flash and a laser pointer. This camerastreams RGB image display data (e.g. 30 Hz) to the FPGA for combinationwith infrared RGB image data and then sends the combined image data tothe display.

The Analog Engine interfaces with and controls the infrared sensor, andstreams raw infrared image data (e.g. 30 Hz) to the DSP. The DSPperforms computations to convert the raw infrared image data to scenetemperatures, and then to RGB colors corresponding to the scenetemperatures and selected color palette. For example, U.S. Pat. No.6,444,983 entitled “Microbolometer Focal Plane Array With ControlledBias,” assigned to the present assignee, is incorporated herein in itsentirety, discloses such an infrared camera. The DSP then streams theresulting infrared RGB image display data to the FPGA where it iscombined with the VL RGB image data and then sends the combined imagedata to the display.

The Embedded Processor Card Engine includes a general-purposemicroprocessor that provides a graphical user interface (GUI) to thecamera operator. This GUI interface consists of menus, text, andgraphical display elements that are sent to the FPGA, where they arebuffered in SRAM and then sent to the display.

The MSP430 interfaces with the user interface including camera buttons,mouse, LCD backlight, and the smart battery. It reads these inputs andprovides the information to the embedded processor card engine where itis used to control the GUI and provides other system control functions.

The FPGA drives the display(s) (LCD and/or TV, for example) withcombined visible-light image data, infrared image data, and GUI data.The FPGA requests both the visible-light and infrared image data fromthe VL and infrared camera modules and alpha-blends them together. Italso alpha-blends the resulting display image with the GUI data tocreate a final blended image that is sent to the LCD display. Of coursethe display associated with the embodiments of the invention is notlimited to an LCD-type display. The FPGA operates under control of theDSP, which is further controlled by the embedded processor card engine.The degree of image alpha-blending and the display mode, i.e.picture-in-a-picture, full screen, color alarm and zoom mode, iscontrolled by the user through the GUI. These settings are sent from theembedded processor card engine to the DSP which then configures the FPGAproperly.

Optical Configuration

Embodiments of the invention combine an engine of a real-timevisible-light camera with an engine of a real-time infrared camera closeto each other in the same housing such that the optical axes are roughlyparallel to each other.

The camera according to the embodiments of the invention places theengine or module of a real-time visible-light camera in the housing of areal-time infrared camera. The placement is such that the visible andinfrared optical axes are as close as practical and roughly parallel toeach other, for example, in the vertical plane of the infrared opticalaxis. Of course other spatial arrangements are possible. The visiblelight camera module, i.e., VL optics and VL sensor array, are chosen tohave a larger field of view (FOV) than the infrared camera module. FIG.4 is a diagram showing the optical path and sensor configuration of thecamera. As shown in the diagram, there are two distinct optical pathsand two separate sensors. One for visible-light, and one for infrared.Because the optical paths for the sensors are different, each sensorwill “see” the target scene from slightly different vantage pointsthereby resulting in parallax error. As will be described in detailhereinafter, the parallax error is corrected electronically usingsoftware manipulations. This provides the capability to electronicallycorrect the displayed images for parallax. In certain embodiments, thevisible-light optics and sensor are chosen so that their respectivefield of views (FOV) are different, i.e. one is larger than the other.For instance, in one embodiment, the VL FOV is greater than the infraredFOV. This provides cost effectiveness. Presently, for a given number ofpixel sensors, visible light sensor arrays are much cheaper thaninfrared sensor arrays. Accordingly, for a given field of view andresolution (instantaneous field of view), visible light sensor arraysare cheaper than infrared sensor arrays.

In certain embodiments, the visible light optics are such that thevisible light camera module remains in focus at all usable distances.Only the infrared lens needs focus adjustment for targets at differentdistances.

Parallax Correction and Display Modes

FIG. 5 shows geometrically, the derivation of the parallax equation (eq.1). As can be seen by the equation, parallax can be reduced byminimizing the distance (q) between the visible-light and infraredoptical apertures, and also by choosing short focal length lenses. Thecamera design will typically physically fix (q). In certain embodiments,the focal lengths of the visible-light and infrared lens (f) can bealtered in the field by changing lenses, or using optical systems thatinclude multiple focal lengths or continuous zoom. In the embodimentswith fixed focal length lenses, the focal lengths remain constant duringoperation once the lenses are installed. Hence, during camera operation,parallax is simply a function of distance (d) to the target. In theembodiment shown, the focal length (f) of each lens is the same. Inalternate embodiments, the focal lengths (f) of the infrared lens andthe visible lens may differ from each other.

The camera corrects the visible-light and infrared images for parallaxand provides several different methods to display the registered imagesto the operator. These methods are described below. In general, parallaxerror corrections are based on the infrared focus distance as will bedescribed hereinafter. However, parallax error may also be corrected bydetermining the distance from the target image (other than via focusdistance) by schemes known to those of ordinary skill in the art.

The camera according to the embodiments of the invention can operate inone of three display modes; 1) full screen visible, infrared and/orblended, 2) picture-in-a-picture such as partial infrared image in afull screen visible image, and 3) infrared color alarms in visible-lightimages. In any one of these display modes, temperatures will be recordedand can be displayed in the infrared portion of the image. Temperaturescan also be displayed on a visible-light only image from the recordedbut not displayed infrared image.

In the full screen display mode, an operator has a choice of selectingfor display a full screen visible-light only image, a full screeninfrared only image, or a full screen blend of visible-light andinfrared images. In an embodiment of the invention, the display is about320 by 240 pixels and is represented by the dashed-line box shown inFIG. 6. The infrared sensor has 160 by 120 pixels and the visible-lightsensor has 1280 by 1024 pixels. These particular dimensions are given byway of example and are not limiting to any of the embodiments of theinvention. Thus, the infrared sensor, the VL sensor and display may eachbe individually larger or smaller than the particular examples given.FIG. 6 shows a diagram of the mode where the full 160 by 120 infraredimage is interpolated to fill the camera display. Based on the displaymode chosen, a portion of the 1280 by 1024 visible-light image iswindowed to match the infrared window. Since the number of selectedvisible-light sensor elements does not necessarily match the 320 by 240pixels of the camera display, the visible-light image is scaled to matchthe camera display. After parallax error correction, each resultinginfrared display pixel will represent the same instantaneous field ofview (IFOV) as its corresponding visible-light display pixel. Becausethe two images are matched, the camera operator can easily identifypoints-of-interest in the infrared image with objects in thevisible-light image simply by noting where the features of interestoverlie each other in the two images. In the embodiment shown in FIG. 6,the display mode is entitled “Full-Screen, Full-Sensor Infrared andFull-Screen, Partial-Sensor Visible-Light display mode.” Additionaldisplay modes are discussed further below.

As the number of pixels of the infrared sensor is reduced, any resultinginfrared image will become course. However, certain embodiments of theinvention increase the utility of even small infrared sensor arrays. Forinstance, an 8 by 8 array may be considered too course to provideinfrared imagery that matches visible light imagery in the Full-Screen,Full-Sensor Infrared and Full-Screen, Partial-Sensor (or Full-Sensor)Visible-Light display mode. In the embodiment shown in FIG. 6A, however,the IFOV of the infrared display pixel is left much larger than itscorresponding visible light display pixel. FIG. 6A shows the substantialdifference between the IFOV of the infrared and visible light pixelswhen in the Full-Screen, Full-Sensor Infrared and Full-Screen,Partial-Sensor (or Full-Sensor) Visible-Light display mode. The infraredpixels 250 of the 8 by 8 pixel array are shown in FIG. 6A by dottedlines and have been scaled to fit the entire display 252 screen. Thedisplay 252 is, for example, about 320 by 320 pixels and is representedby the solid-line box shown in FIG. 6A. The infrared sensor has 8 by 8pixels and the visible-light sensor has 1280 by 1024 pixels. Based onthe display mode chosen, a portion (or all) of the 1280 by 1024visible-light image is windowed to match the infrared window. Since thenumber of selected visible-light sensor elements does not necessarilymatch the 320 by 320 pixels of the camera display, the visible-lightimage is scaled to match the camera display. After parallax errorcorrection, if necessary, the resulting infrared display pixel in FIG.6A will represent a much larger IFOV than its correspondingvisible-light display pixel. Accordingly, as shown by the sample displayscreen in FIG. 6B, the relatively high pixel count of the visible lightsensor provides clear visible light imagery that allows quickidentification of relevant physical features within the image. Eventhough the thermal data is overlayed in an 8 by 8 matrix as shown inFIG. 6B, the thermal data 254 may be provided to the user in severaldifferent manners in this embodiment. For instance, the thermal data 254may represent the hottest two thermal pixels in order to identify thehotspots in the visible image. The thermal data 254 may also provideindications that these two pixels meet the alarm conditions as discussedfurther below when the camera is operated within any of the alarm modes.Radiometric functionality may still be applied to these pixels such thatthe actual sensed temperature (e.g., an average within the IFOV) of thehottest pixel or the center pixel (or centrally located pixels) may bedisplayed.

Again, these particular dimensions provided for the embodiments shown inFIGS. 6A and 6B are given by way of example and are not limiting to anyof the embodiments of the invention. Thus, the infrared sensor, the VLsensor and display may each be individually larger or smaller than theparticular examples given. For instance, the infrared sensor array inthis embodiment may be 1 pixel, 2 by 2, 4 by 4, 8 by 8, 16 by 12, etc.Moreover, in some embodiments, the infrared sensor may be provided byinexpensive, low pixel count, thermopile arrays (e.g., 2 pixels to 1024pixels).

Parallax error between the visible-light image and the infrared image iscorrected automatically by the camera. This process is referred to asregistering. In order to apply the proper parallax correction, thecamera must first determine the distance to the target object ofinterest. One method to determine the target distance is to sense thefocus position of the infrared lens using a Hall-effect sensor. FIGS. 7and 8 show a sectional view of camera 10 taken from front to rearthrough the center of infrared lens 14. Referring to FIGS. 7 and 8, aHall-Effect sensor 30 is fixed in the housing 32 with respect to theinfrared sensor array 34 to sense the proximity of a magnet 36 attachedto the back of the IR lens 14. As the focus of the lens is changed viarotation of focus ring 16, the distance f′ between the magnet 36 and theHall-Effect sensor 30 changes, resulting in an output from theHall-Effect sensor that is proportional to focus position. (The focus ofthe lens could be changed by moving the lens or moving the infraredsensor array.) This focus position is used to derive an estimate of thedistance to the target. The infrared lens focus position provides anespecially convenient estimate of distance because typical infraredlenses have a low F-number, resulting in a shallow depth of field. TheHall-Effect sensor may, in one embodiment, be fixed on the infraredsensor array. In addition, the positions of the Hall-Effect sensor andmagnet may be reversed from that shown.

In the embodiment shown in FIGS. 7 and 8, the magnet 36 is a ring thatencircles an interior surface of the focus ring 16 facing the infraredsensor array 34. The Hall-Effect sensor 30 is fixed in the camerahousing 32 a small distance from of the infrared sensor array 34. Thedistance between the Hall-Effect sensor and the magnet represents thedistance f′ shown in FIGS. 7 and 8. FIG. 7 shows the lens positioned fornear focus and FIG. 8 shows the lens positioned for far focus in whichcase the magnet is closer to the Hall-Effect sensor than in FIG. 7.Mechanisms and methods other than those described above for a Halleffect sensor may, of course, be employed to determine the distance totarget. Such equivalent mechanisms or methods would be known to thosewith skill in the art. The Hall-Effect sensor is one convenient method.

Estimating the distance between the target and the camera is a valuablesafety feature. For example, OSHA has specific safety distancerequirements when inspecting high voltage electrical cabinets. Thus,using the camera according to the embodiments of the invention, one candisplay the distance to the target on the display so that the cameraoperator is assisted in complying with OSHA's safety requirements.

In addition, it can be valuable to know the size of the spot on thetarget that is being measured (instantaneous field of view spot size).Because the spot size is a function of distance and the embodiments ofthe invention have the ability to measure (or rather estimate) distancethat is needed to correct parallax error, spot size can be calculated asa function of distance and displayed to the camera operator via thedisplay.

The lens position sensor value to focus distance correlation for eachinfrared lens is determined at the factory and stored with other cameracalibration data in the camera's non-volatile memory. This calibrationdata includes X and Y image offsets calculated for each focus distance.By utilizing the sensed infrared lens focus position and the factorycalibration data, the correct X and Y sensor offsets of the partial areafrom the visible-light sensor to be displayed can be computed and usedto select the appropriate visible-light sensor area for the currentinfrared focus distance. That is, as the focus distance of the infraredlens is changed, different areas of the visible-light sensor image areextracted and displayed, resulting in registration of the infrared andvisible-light images for objects at the focus distance. FIG. 9 showscombined picture-in-a-picture display of visible-light and infraredimages misaligned, i.e. uncorrected for parallax error. FIG. 10 showsthe same images corrected for parallax error. Referring to FIG. 9, thecenter quarter of the display shows a blurry (unfocused) andunregistered infrared-only image 40 placed within the surroundingframework of a visible only image 42. The rectangular dark sections 44in the image are misaligned (unregistered) showing the parallax errorresulting from the unfocused infrared image 44. Referring to FIG. 10,the rectangular dark sections 44 in the infrared image 40 are registeredwith the portions of such sections 44 in the visible only image 42,showing that infrared image is now properly focused. FIGS. 9 and 10highlight a method by which a user of camera 10 could focus the infraredimage 40 by merely rotating focus ring 16 until image 40 is properlyregistered. Although FIGS. 9 and 10 show the center quarter of thedisplay as infrared only, this same method and technique could be usedfor a blended visible and infrared image, whether the images are shownpicture in picture, full display, alarm mode, or other display modes.

Note that objects within the scene that are not at the focus distancewill still exhibit a parallax error. Nearer objects will exhibit alarger parallax error than objects beyond the focus distance. Inpractice, parallax error becomes negligible beyond a focus distance ofapproximately 8 feet for lenses used with typical infrared cameras. Alsonote that parallax errors can only be corrected down to a limited closefocus distance to the camera (typically about 2 feet). This distance isdetermined by how much “extra” field of view the visible-light sensorprovides as compared to the infrared sensor.

When an image is captured, the full visible-light image and the fullinfrared image with all of the ancillary data are saved in an image fileon the camera memory card. That part of the visible-light image notdisplayed which lies outside of the camera display dimensions when theimage was taken is saved as part of the visible-light image. Later, ifan adjustment in the registration between the infrared and visible-lightimage is needed, either in the camera or on a computer, the fullvisible-light image is available.

The camera allows the operator to adjust the registration of thevisible-light and infrared image after an infrared/Visible-light imagepair is captured and stored in memory. One way to accomplish this is touse the infrared lens position as an input control. This allows theoperator to fine-tune the registration, or to manually register objectsin the scene that were not at the infrared focus distance when theimages were captured, simply by rotating the focus ring on the lens.

The visible-light image, when it is the only displayed image, isdisplayed preferably in color, although it need not be. When it isblended with the infrared image, the visible-light image is converted togray scale before it is blended so that it only adds intensity to thecolored infrared image.

FIG. 11 shows the scene display mode entitled “Partial-Screen,Full-Sensor Infrared and Full-Screen, Partial-Sensor Visible-Lightdisplay mode.” In this mode, the camera uses all of the availableinfrared sensor elements to provide an infrared image that fills only acentral area of the camera display. Standard image processing techniques(e.g. scaling and windowing, for example) are used to fit the infraredimage into the desired area of the display. The IFOV of thevisible-light image is adjusted to match the IFOV of the infrared imageand then a portion of the visible-light image is selected to fill thefull display and to match the infrared image in the center of thedisplay. The center quarter of the display can be infrared only,visible-light only or a blend of the two. The remaining three-quartersof the display (outer framework) is visible-light only.

The camera uses the same technique in this mode as that described forthe full screen mode to correct for parallax.

Alternatively, instead of matching the visible-light image to theinfrared image just the opposite may be done. FIGS. 12 and 13 illustratethis technique. FIG. 12 shows a picture-in-a-picture “Partial-Screen,Partial-Sensor infrared and Full-Screen, Full-Sensor Visible-Light scenedisplay mode.” In this mode, the camera uses all of the visible-lightsensor elements to fill the display. If the number of visible-lightsensor elements does not match the number of display pixels, the camerauses standard imaging techniques to create an image that fills thedisplay screen. A portion of the available infrared sensors is chosen toprovide the infrared image. The infrared image is windowed and matchedso that the resulting infrared display pixels provide the same IFOV asthe visible-light image display pixels.

The camera uses similar techniques to those described for FIG. 6 tocorrect for parallax. However, in this mode, different areas of theinfrared sensor are selected to match the center region of thevisible-light image as the infrared focus distance is changed. Note thatin this mode, the infrared image is always displayed in a fixed positionin the middle of the display.

FIG. 13 shows the “Partial-Screen, Full-Sensor infrared and Full-Screen,Full-Sensor Visible-Light scene display mode.” In this mode, the camerauses all of the infrared and all of the visible-light sensor elements toconstruct the displayed images. The visible-light image is scaled tocompletely fill the display. The infrared image is windowed and scaledso that the IFOV of the resulting display pixels match the visible-lightimage. The resulting image is displayed over the matching area of thevisible-light image.

Like the previously described mode, parallax is corrected by moving theinfrared image scene to align it with the visible-light image scene.

Alpha-Blending

Alpha-blending is a process of ratioing the transparency/opaqueness oftwo images superimposed on one pixel. If the Alpha=maximum, then thefirst image is opaque and the second is transparent and is so written tothe display. If Alpha=0, then the first image is transparent and thesecond image is opaque and is so written to the display. Valuesin-between cause ‘blending’ (alpha blending) between the two sources,with the formula Display=Source 1*(Alpha/max_Alpha)+Source2*((max_Alpha-Alpha)/max_Alpha).

FIGS. 14-16, show respectively, an infrared only image of an insulatedcup, a visible light (VL) only image of the cup, and a partialalpha-blending of the infrared and VL images.

The camera will enable the operator to adjust the alpha blending of thevisible and infrared images from the extremes of infrared-only (FIG. 14)or visible-only (FIG. 15) to any combination of alpha blending betweenthese two extremes (FIG. 16). Note that although the infrared image isnot visible in FIG. 15, the underlying infrared image data is used todisplay the correct object temperature 52 in the visible light image.Thus, as the cursor is moved over the visible-light image, thetemperature 52 associated with the cursor's location on the image isdisplayed.

The infrared and visible-light images can be displayed in either coloror grayscale. When color is used to portray temperatures in the infraredimage, the visible image in the overlap area can be displayed ingrayscale only so that it doesn't excessively corrupt the infraredpalette colors.

When an image is saved, both the visible and infrared images are savedindividually so reconstructing images with different alpha blending canbe accomplished later either in the camera, or with PC software.

Alarm Modes

The camera supports several different visual alarm modes. These modesare used to call the operator's attention to areas of interest in thevisible-light image by displaying an alpha-blended or infrared onlyimage in areas that meet the alarm criteria as set by the user. FIG. 17shows an example of the “hot threshold” alarm mode. Only those pixels inthe infrared image that exceed a set temperature threshold (hotspots 60)are displayed. In the color alarm mode, the visible-light image 62 isswitched to gray scale so that the infrared image stands out with noambiguity. The camera can provide alarm modes, such as those describedbelow. Other alarm modes are also possible.

-   -   Absolute hot threshold—infrared pixels above a defined        temperature are alpha-blended with corresponding visible-image        pixels.    -   Absolute cold threshold—infrared pixels below a defined        temperature are alpha-blended with corresponding visible-image        pixels.    -   Relative hot threshold—A temperature range is defined by the        user. The temperature range is relative to the current hottest        pixel (or average of a set number of hottest pixels) in the        scene or from a previous scene or reference scene. Infrared        pixels above the threshold defined by the current hottest        pixel(s) in the scene minus a user defined or predetermined        temperature range are alpha-blended with their corresponding        visible-image pixels. For example, if the temperature range is 5        degrees, and the current hottest pixel(s) in the scene is 100        degrees, for example, all infrared pixels above 95 degrees in        the scene will be alpha-blended with corresponding visible-light        pixels.    -   Relative cold threshold—A temperature range is defined by the        user. The temperature range is relative to the current coldest        pixel (or average of a set number of coldest pixels) in the        scene or from a previous scene or reference scene. Infrared        pixels below the threshold defined by the current coldest        pixel(s) in the scene plus a user defined or predetermined        temperature range are alpha-blended with their corresponding        visible-image pixels. For example, if the temperature range is 5        degrees, and the current coldest pixel(s) in the scene is 10        degrees, all infrared pixels below 15 degrees in the scene will        be alpha-blended with corresponding visible-light pixels.    -   Absolute range (isotherm)—The operator enters a temperature        range. Infrared pixels with a temperature within the set range        are alpha-blended with their corresponding visible-light pixels.        For example, the user enters a range of 80-100 degrees. All        infrared pixels with a temperature value within the 80-100        degree range are alpha-blended.    -   Alarm flash mode—To further call attention to areas of interest,        the camera may provide a mode whereby the alpha-blended areas        are “flashed” by alternately displaying the alarmed pixels as        visible-light only, and then either alpha-blended or infrared        only.

The alarm modes identified above may also be indicated audibly or viavibration. Such audible or vibrational alarms may be useful insituations where hotspots are small enough to otherwise go unnoticed inthe visual display. In embodiments that include audible or vibrationalarms, the camera can generate such an alarm to alert the cameraoperator when, for instance, the camera detects an out of specificationtemperature or any of the other alarms modes identified above. Referringback to FIG. 3, the camera may include an alarm module connected to theFPGA that provides audible or vibrational alarms. The vibrationmechanism can be similar to that used in cellular phones to alertpersons of an incoming call.

Audible alarms may also be used to identify different camera operatingconditions. For instance, specific pitches may be used to indicate thebattery charge level, when the camera is initially powered-on, powereddown, entering sleep-mode, or recovering from sleep-mode. The pitchesfor such operating conditions may be stored in camera memory.

An audible alarm may also be used to indicate the quality of the focussetting. For instance, the camera may include a known autofocusmechanism. The autofocus mechanism may include a known autofocusalgorithm that analyzes the sharpness of image edges and the contrast ofan edge. It is known that the output of this algorithm supplies acontrol signal to the autofocus system. This same output could be usedto drive the pitch of the audible alarm to indicate when the camera isin or out of focus.

Audible alarms with varying outputs may also be used in differentembodiments. The variation in output may include variable pitch ornotes, a variable frequency of a single pitch or pulse, similar to aGeiger counter, or other known variable audio outputs. The variation inoutput can indicate to the user the relative level of the alarm. Forinstance, in some embodiments, higher pitches may indicate that thecamera has sensed hotter temperatures. Lower pitches (or pulsefrequencies, in other embodiments) may indicate that the camera hassensed cooler temperatures. Moreover, the camera may increase the pitchof the output emitted as the sensed temperature increases. That is, ifthe current hottest pixel in the scene exceeds the absolute threshold orthe range in the absolute range, the camera would emit an alarm tone.The amount by which the hottest pixel exceeds the absolute threshold orthe range in the absolute range would dictate the pitch of the alarmtone emitted. The more the hottest pixel exceeds the threshold or upperrange amount, the higher the pitch. Similarly, as the temperature of thecurrent hottest pixel increases, the camera would in turn increase thepitch of the alarm tone emitted. The camera may operate similarly forlow temperatures. If the current coldest pixel in the scene falls belowthe absolute threshold or the range in the absolute range, the camerawould emit an alarm tone. The amount by which the hottest pixel fallsbelow the absolute threshold or the range in the absolute range woulddictate the pitch of the alarm tone emitted. The more the hottest pixelfalls below the threshold or lower range amount, the lower the pitch.Similarly, as the temperature of the current hottest pixel decreases,the camera would in turn decrease the pitch of the alarm tone emitted.The same type of alarm system may be provided by variation of alarmpulse frequencies. The pitch or frequency connotes certain informationto the user in either embodiment, such information may signify animportant alert or merely certain operational data as described above.

PC Software

All of the image display techniques described for the camera can also beimplemented in software that runs on a PC host computer and can beapplied to images captured by the camera.

ADVANTAGES

The advantages have already been stated above. The infrared image willnot only be sharper with much more detail, it will be surrounded with avisual image showing exactly what and where the infrared targets are.Parallax error will be automatically corrected, yielding a visible-lightcontrol image that is correctly registered with the infrared image.Infrared cameras can be made with smaller less expensive detectorarrays, yet display the apparent detail and contrast of very expensiveinfrared cameras with large and ultra-sensitive detector arrays. FIG. 18shows a typical infrared image of a low infrared contrast scene. FIG. 19shows the same scene with an alpha-blended visible-light image, yieldinga much higher apparent contrast with target site temperaturemeasurement.

Uses

This camera can be used in all phases of infrared thermography wherecurrent infrared cameras are used today and in the future. In the caseof the simplest uses such as an electricians tool, the camera can bemade inexpensively with a small infrared detector array and yet havevery high performance—high image quality with high spatial resolutionand accurate temperature. In the case of high-end thermography thecamera can be made at a lower cost and have images with greater apparentdetail than the most expensive infrared cameras. The camera willeliminate the need to take separate visible-light images to be includedin thermography reports.

Laser Pointer

Various applications are possible using the laser embodiments of thepresent invention. As previously mentioned, because the laser pointerradiation is in the visible spectrum, it is not visible in the infraredimage. As a result, the laser pointer is of limited value in infraredcameras. This is problematic when the location of a hot or cold spot isdifficult to identify. For example, large industrial control panelsoften have many components that are similar in shape and packed tightlytogether. It is sometimes difficult to determine the exact componentthat is causing a hot spot in the infrared camera image. In addition, inbuilding inspection applications where a wall appears uniform in thevisible image but shows a defect in the infrared image, the laserpointer of the embodiments of the invention can be used to identify theexact location of the defect on the wall. For roof leak detectionapplications, it can greatly aid the thermographer in marking the areasuspected of needing repair. The camera operator can outline the wetarea by adjusting the camera pointing so that the laser spot seen in theimage outlines the suspected wet area in the image and thus alsooutlines the suspected wet area on the roof with the laser beam so thatit can be correctly marked. In an R&D application where the target iscomplex such as a printed wiring board assembly, the laser pointerembodiments of the invention may aid in identifying the location of theinfrared point of interest.

The laser pointer of the embodiments of the invention is used toaccurately identify the location of infrared points-of-interest and toeasily aid the focusing of the infrared optics. FIGS. 24-26 show anassociated sequence of events. The laser pointer can be turned on usingone of the camera's programmable buttons or by other mechanisms by thecamera operator. At a reasonable distance, the laser pointer spot 100 onthe target can be seen in the visible-light image (FIG. 24) and in theblended visible-light and infrared image that has been corrected forparallax error (FIG. 25). As noted above, the correction for parallaxerror registers the IR imagery with the VL imagery on the display.Because the laser pointer is mounted so close to the VL lens, as shownin FIG. 1, correction for parallax between the IR and VL imagery alsoeffectively corrects any parallax error between the IR imagery and thelaser pointer. Once the laser spot is identified in the blended image(FIG. 25), the camera operator can adjust the camera pointing until thelaser spot in the blended image matches the spot of interest 102 in theinfrared image (FIG. 26). The laser beam then marks the target at thepoint-of-interest (FIG. 26). This occurs, of course, because thecorrection for parallax error between the IR and VL imagery alsocorrected the parallax error between the laser pointer and the IRimagery.

Because the camera according to the embodiments of the invention hasbeen calibrated in the factory to identify the location of the laserspot in the infrared image using parallax calibration data as a functionof infrared camera module focus distance, the camera operator does notneed to see displayed the laser spot in the VL image. If the target isat a distance and/or has a low reflection for the laser wavelength, thelaser spot may be too weak for the VL camera to show prominently on thecamera display but it can still be seen on the target by the humanobserver. FIGS. 27 and 28 show an associated sequence of events. In thiscase, the infrared focus is adjusted as normally done by observing thesharpness of the infrared image. A computer-generated laser spotreference mark 200 is registered with the infrared image so that arepresentative mark (e.g., circle) is displayed on the infrared image(FIG. 27). The camera operator then adjusts the camera pointing untilthe laser calibration mark 200 lies over the infrared point-of-interest202 (FIG. 28). Once that happens, the laser beam then strikes the targetat the point of interest.

Alternatively, the camera operator first focuses the infrared imageusing an infrared display image only, switches to the visible-lightdisplay where the laser 210 will be shown in the display as seen in FIG.20. The operator marks the laser spot 210 on the display with a marking212 such as a circle (see FIG. 21) and then switches the display back tothe infrared only (see FIG. 22) where the marking 212 is registered withthe infrared image and it is displayed on the infrared image, positionedin the center quarter of the display area. This occurs, of course,because the correction for parallax from focusing the infrared imagealso corrected the parallax error between the infrared image and thelaser pointer, since the laser pointer is mounted very closely to the VLlens as shown in FIG. 1. Accordingly, the laser pointer projects along atrajectory approximately equal to that of the optical axis of the VLlens. The operator then adjusts the camera pointing so that the mark 212on the infrared display matches the thermal spot of interest 214 on theinfrared display. (see FIG. 23) Once that happens, the laser beam thenstrikes the target at the point of interest.

Using the Laser Pointer to Focus the Infrared Image

With calibration data correcting for parallax between the laser pointerand the infrared image and the ability to see the actual laser spot inthe VL image, a process for monitoring and aiding the infrared focus ispossible. FIGS. 29 and 30 show an associated sequence of events. In thiscase, the location of the laser spot 220 is visible in the VL image(FIG. 29). The camera according to the embodiments of the invention hasbeen calibrated in the factory to generate a computer-generated laserspot reference mark 222 that indicates the location of the laser spot ina focused infrared image using parallax calibration data as a functionof infrared camera module focus distance. This reference mark may bedisplayed in the IR image or the VL image (that overlaps the IR image).In FIG. 29, the reference mark 222 is shown in the VL only image. As theinfrared lens is adjusted, the mark moves in the VL image showing thespot where the laser dot would be in the infrared image. When theinfrared mark is coincident with the laser dot seen in the VL image(FIG. 30), the focus adjustment may stop and the infrared camera moduleis in focus. This allows the most novice operator to focus the infraredlens and eliminates the subjective nature of focusing.

What is claimed is:
 1. A camera for sensing infrared (IR) images,comprising: an array of IR detectors for sensing IR images of a targetscene; an alarm module for providing an audible alarm when a portion ofthe sensed IR images meets at least one user-defined alarm criterion andnot providing the audible alarm when no portion of the sensed IR imagesmeets the at least one user-defined alarm criterion, the alarm beingemitted with a tone of variable output, the variation of the output toneindicating the relative level of the alarm; and a display configured todisplay the sensed IR images and visually indicate portions of thesensed IR images that meet the user-defined alarm criterion.
 2. Thecamera of claim 1, wherein the alarms are emitted with a tone ofvariable pitch, higher pitches indicating that the IR detectors havesensed relatively hotter temperatures and lower pitches indicating thatthe IR detectors have sensed relatively cooler temperatures.
 3. Thecamera of claim 1, wherein the alarms are emitted with a tone ofvariable frequency, an increase in frequency of the tone indicates thatthe IR detectors are sensing a hotter target scene.
 4. The camera ofclaim 1, wherein the alarm module provides a first audible alarm when aportion of the sensed IR images meets at least one user-defined alarmcriterion and emits second audible alarms to signal one or more cameraoperating conditions, the second audible alarms being distinguishablefrom the first, and wherein the one or more camera operating conditionsinclude at least one of the battery charge level, when the camera isinitially powered-on, powered down, entering sleep-mode, or recoveringfrom sleep-mode.